Power amplifiers exhibit non-linear behavior in the presence of amplitude-modulated radio frequency (RF) signals. The non-linear behavior produces distortion products. For many RF transmitter applications, linearization schemes are used to reduce power amplifier distortion sufficiently to meet system requirements for co-channel interference. Digital pre-distortion is a commonly employed linearization scheme. In digital pre-distortion, the input signal to the power amplifier is pre-distorted in such a manner that the input signal to the power amplifier represents the inverse of the non-linear characteristic of the power amplifier. Thus, a cascade transfer function of the digital pre-distorter and the power amplifier is linear.
For many RF communication systems, the requirements on instantaneous signal bandwidth (ISBW)/video bandwidth (VBW) of the power amplifier is continually increasing as requirements on system data throughput are continually increasing. Limited VBW introduces memory effects that impair the performance and/or increase required complexity of digital pre-distortion linearizers. For example, the VBW of a device may be directly affected by the low frequency resonance (LFR) caused by interaction between bias feeds and output circuits that are electrically connected between active devices and an output lead. Power amplifiers with significant memory effects thus rely on pre-distortion signals applied to the input also containing the inverse of the memory characteristics, thereby increasing the complexity and power consumption of the pre-distorter. Such complications can also limit the extent to which the system is capable of cancelling unwanted distortion products. Consequently, increasing VBW of a power amplifier reduces the complexity and power consumption of the digital pre-distorter and may also improve overall transmitter performance.